In the continuous casting of metal, molten metal is delivered from a molten metal receptacle, such as a ladle or tundish, to a continuous caster through a discharge nozzle located in the bottom of the molten metal receptacle. A layer of slag comprising metal impurities rides above the top surface of the molten metal within the molten metal receptacle. As the molten metal is discharged from the nozzle it is important to maintain the separation between the slag and molten metal so that the molten metal being discharged is not contaminated by the slag.
The flow of molten metal through the discharge nozzle forms a vortex in the molten metal immediately above the nozzle. If the level of molten metal within the molten metal receptacle is sufficiently high the vortex does not affect the separation of the molten metal and slag. When the molten metal reaches a predetermined critical level, however, the vortex pulls down the slag layer through the center of the vortex and into the nozzle along with the molten metal. As a result, the metal is contaminated by the slag.
A slag control body is operative to inhibit the formation of a vortex in the molten metal. The slag control body is constructed of a refractory material having a density heavier than that of the slag and lighter than that of the molten metal so that the slag control body will tend to sink below the slag layer yet remain above the surface of the molten metal. When the molten metal reaches a predetermined critical level, the slag control body is drawn by the vortex into the nozzle and lodges in the nozzle to obstruct further flow.
A number of transfer and release methods and apparatuses have been developed in the prior art for introducing the slag control body into the molten metal receptacle. One such method is to have an operator climb to the top of the molten metal receptacle by means of a staircase, or the like, located adjacent the receptacle and at the required time drop the slag control body into an opening in a top end portion of the molten metal receptacle. The height of the ladle and the weight of the slag control body make such a task inconvenient and undesirable. Moreover, the high temperatures associated with the molten metal process expose the operator to a hazardous environment.
Overhead cranes have been used to drop the slag control body into the molten metal receptacle. The slag control body is often inadvertently subjected to a slight swinging motion as the crane positions the transfer apparatus making it difficult for the operator to assess whether the slag control body is aligned with the opening in the top end portion. This affects the timing and accuracy of the release of the slag control body. The operator must wait until the slag control body stabilizes above the opening in the top end portion. This is inefficient and can slow down the overall molten process. If the operator drops the slag control body while it is still swinging the slag control body may miss the opening or otherwise be misplaced in the molten metal receptacle. This, in turn, can cause the slag to be pulled into the vortex and contaminate the discharged molten metal since the slag control body may not be appropriately or timely drawn by the vortex into the nozzle.
Another prior art apparatus requires the addition of heavy and intricate parts to be mounted onto the top end portion of the molten metal receptacle. Such parts add cost to the transfer apparatus. The parts also add additional weight to the top end portion making transportation or handling of the top end portion from one location to another more difficult. Moreover, because the parts are mounted on the top end portion, they are exposed to rigorous wear due to the high temperatures involved in the molten metal process and are susceptible to being inadvertently damaged during positioning of the top end portion. In any event, the parts eventually require repair and/or replacement, thus increasing costs.
What is needed is a transfer and release apparatus and a molten metal receptacle adapted to cooperate with the transfer and release apparatus, wherein the transfer apparatus automatically releases the slag control body when the transfer apparatus is lowered onto the top end portion and wherein the molten metal receptacle includes means for thereafter guiding the slag control body into the receptacle. Such a transfer apparatus must be operable from a location remote from the slag control body at an easily accessible position and must also be simple and cost-effective to manufacture and assemble, comprise a minimal amount of parts and be capable of handling the rigors often associated with the molten metal process.